Traumatic brain injuries (TBI) affect millions of patients each year worldwide. Cerebral hemodynamic dysfunction is common following TBI, potentially resulting in catastrophic neurologic sequelae, including long-term disability and even death. Current diagnosis and management methods are limited to hospital settings (transcranial Doppler ultrasonography—TCD, CT, MRI, etc.). Accordingly, there is a need for developing a medical device that can provide clinical utility of hospital-based assessment methods outside of a hospital for rapid and reliable assessment using disruptive innovations in TCD ultrasonography.
Various sensory modalities are currently used in major hospitals for the assessment of cerebral hemodynamics within the Circle of Willis arteries of the brain, including TCD ultrasound, transcranial color-coded sonography (TCCS), phased arrays, and functional Near-Infrared Spectroscopy (fNIRS). These modalities emit energy capable of penetrating windows in the skull. Acquiring the cerebral blood flow velocity (CBFV) signals using such sensory modalities, however, requires the placement of a transducer within a specific region of the skull thin enough for the ultrasound waves to penetrate. For example, it is known that a thin skull region often exists superior to the patient's zygomatic arch (transtemporal). Other windows often exist at the suboccipital, transorbital, submandibular portions of the skull. The location of these narrow windows, however, varies significantly from person to person based on facial features, and even race or gender. This variation makes insonating—exposing to ultrasound the desired blood vessel difficult. This difficulty has often restricted TCD use, and other modalities, to major hospitals who engage expert sonographers to operate the device.
TCD specifically has been widely used clinically since the 1980s to measure CBFV within the major conducting arteries and veins of the brain (Circle of Willis). It is currently used in the diagnosis and monitoring a number of neurologic conditions, including the assessment of arteries after a subarachnoid haemorrhage (SAH) for vasospasm, aiding preventative care in children with sickle cell anemia, and risk assessment in embolic stroke patients. TCD utilizes the Doppler effect by emitting ultrasound frequencies typically between 1.6 MHz and 4 MHz and measuring the shift in frequency upon reflection from non-stationary tissue (red blood cells), which are converted to velocity. Depth information within the biologic tissue is controlled by time delays between emitting and receiving of the ultrasound waves.
Fully automating TCD use would not only remove the need for an expert technician but also open the technology up to a broader range of clinical indications. As such, there is a need for developing a portable, fully automated system to determine appropriate window locations.
Existing semi-automated diagnosis methods typically use two degree of freedom robotic mechanisms that can only reorient the TCD probe with pan and tilt rotations, emitting energy into the skull and then analyzing the return signals, but are otherwise unable to traverse portions of the skull in X and Y directions. All existing semi-automated methods require a knowledgeable user to place the robotic mechanism on an existing window. If such an existing mechanism is not placed on an existing window, useful data will not be returned. Some existing two degree of freedom mechanisms will not always find a signal, when they do, it often takes a trained technician to determine the location of appropriate windows and the best signals. Further, some existing mechanisms are not capable of constructing a map of blood vessels in the brain. As such, there exists a need to develop a fully automated robotic system that does not require user feedback to locate appropriate windows and is capable of constructing a map of blood vessels in the brain more quickly than current solutions.